Prevalence of the skin lesion acanthosis nigricans was determined in two tribal communities in Texas and Nebraska. Thirty-eight percent of the Alabama-Coushatta tribe of Texas had acanthosis nigricans. Nineteen percent of Omaha and Winnebago tribal children had the skin lesion; the youngest children had the least acanthosis nigricans. Among weight-matched Alabama-Coushatta, fasting insulin concentrations were twofold higher in subjects with the lesion. It was concluded that acanthosis nigricans is highly prevalent among Native Americans and that its presence suggests insulin resistance. Thus, it may identify those with the highest risk for non-insulin-dependent diabetes mellitus in this population.